The proposed work, utilizing the considerable existing technical resources and favorable biological properties of Drosophila, should make a substantial contribution to the understanding of steroid hormonal regulation of gene expression. It would be difficult to overstate the significance and potential applications, both scientific and clinical, of insight into eucaryotic gene regulation in general and steroid hormone action in particular. The investigation of ecdysteroid action during Drosophila development will focus initially on the induction of adult differentiation of imaginal discs. This well characterized example of hormone response allows the coupling of detailed molecular analysis with hormone response in vivo and in vitro. The expected components of a steroid hormone mediated system of gene regulation are the hormone receptor, genes with modified transcription, and mediators of later steps in the sequence of hormone induced modulation of gene expression. the specific aims of the experimental work are (1) the purification of hormone receptor and preparation of monoclonal antibody to receptor, (2) the purification of two non-histone chromosomal proteins which exhibit increased synthetic rates in response to hormone, good candidates for mediators of later steps in hormone response, and preparation of monoclonal antibodies to these proteins and (3) identification and isolation of cDNA and genomic clones for hormone responsive sequences in imaginal discs. The timing and extent of gene expression and the cellular distribution of these gene products during imaginal disc differentiation will be determined, providing insights into hormone action in this developing tissue. The antibodies and clones for molecules specific for imaginal disc response will be used to investigate the tissue specificity of ecdysteroid response. Other Drosophila tissues will be screened for the presence of these gene products and, if present, for the temporal pattern of expression, quantity and cellular distribution of the gene products. A comparative analysis should identify both molecular components common to ecdysteroid responding tissues and tissue specific components, and thus elucidate the molecular mechanism of steroid hormone regulation of gene expression.